Efforts to obtain increased energy density of battery cells highlight a need for electrochemical techniques as well as additional characterization methods for these cells in order to meet user needs and safety requirements. In particular, a continuing need has called forth inventive efforts for developing novel calorimeters to satisfy various requirements for requiring activities including high energy density systems such as chemical energy storage systems, propellant, explosive, and pyrotechnic devices. To support optimization of electro chemical energy storage systems in particular it is necessary to understand their thermal characteristics at rest and under prescribed charge and discharge cycles. In one example, a need existed to develop a calorimeter system able to accommodate multiple battery cell configurations and provide empirical system data for use in modeling and simulation. Heat capacity, and thermal efficiency for each battery cell were determined, as well as the actual heat load from each surface of the cell. The heat flow from each of six surfaces of the cell and overall thermal efficiency were obtained with the cell at rest and under a variety of prescribed charge and discharge cycles representative of typical usage of these cells. Testing was completed isothermally at 25° C. to capture the requirements necessary to remove the entire generated thermal load from the battery cell. Moreover, these needs also included a requirement to create testing systems which are capable of larger testing capabilities that necessarily includes a need to use larger systems, create more testing options with respect to samples under test, and create an ability to more cost effectively repair or replace costly components in such test systems which existing systems do not accommodate in a cost or time effective manner. As systems are scaled up in size, there is a higher level of failures in system components which require new designs to accommodate repairs or maintenance rather than throwing out large sub-assemblies. Also, there is a need to be able to swap out components for greater customized design or configurability of testing systems with respect to desired testing processes or data collection.
As an example of one embodiment, an improved measuring cell for a temperature bath was designed and constructed to measure the heat flow of larger cells (e.g., 18×8×16 cm). Heat flows from 0.01 to 7.00 Watts were measured with an average signal noise less than 1 mW. In one example, heat capacities of samples were also determined with experimental deviation of less than 2%.
Embodiments of the invention can include apparatus and methods for providing flexible and repairable testing capabilities for systems that generate or absorb heat such as energy storage systems. One embodiment can include a temperature bath structure adapted to contain and maintain a fluid bath at a predetermined temperature, an outer containment structure adapted to insert into the temperature bath structure, heat sinks, thermal sensor assemblies, an internal containment structure, and thermal barriers between different elements of the invention to isolate different sections from each other. An embodiment of the invention can include a system where the thermal sensor assemblies and heat sinks removeably attach to different sections of the inner containment structure so as to measure heat flow into or out of the inner containment structure's different sections without being altered by direct thermal contact with other inner containment sections. Embodiments of the invention permits rapid insertion/removal of samples as well as replacement of sections of an exemplary system including embodiments or parts of the thermal sensor assemblies as well as providing an ability to obtain separate thermal measurements associated with different sections of a sample under test within the inner containment structure. Other aspects of the invention include a capability to insert or substitute existing components such as containment structure elements, thermal sensors etc. with different sized elements or structures to accommodate different types of samples or differently sized samples under test. Embodiments can include electrical bus or wiring structures such as separate wiring sections and quick disconnects that also permit rapid repairs or alteration of configurations of various aspects of embodiments of the invention.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrative embodiment exemplifying the best mode of carrying out the invention as presently perceived.